The Core will contribute to the Center's expertise in the study of HIV epidemics as the unit of analysis, and provide opportunities to CDUHR investigators to develop research proposals to examine HIV transmission dynamics, primarily in international settings. Through their collaborations with the World Health Organization Multi-Site Study of HIV and Drug Use and long-term studies of the HIV epidemics in New York and Bangkok, the staff of the Core can serve as a resource and foster new research to address emerging epidemics.